The present invention relates to golf club shafts and a process for manufacturing same.
From the past, a fiber-reinforced hollow plastic golf club shaft (referred to hereinafter simply as the shaft) is known which has a structure such that an inner layer made of a wound-fiber-reinforced plastic and an outer layer formed thereon and made of a wound-fiber-reinforced plastics are bonded integrally.
In the prior art shaft having such a structure, it was ordinary that the orientation angle (absolute value, same in the following) of the wound-fibers was larger in the outer layer than in the inner layer and that in both layers the angle was gradually increased from the small diameter portion (the top end portion) toward the larger diameter portion (the grip portion). In the golf club shaft of such a structure, however, its kick point is determined to a fixed point depending on the length of the shaft and cannot be adjusted.
On the other hand, a method for adjusting the thickness of the resin in the intermediate portion (Patent Appln. No. Sho. 53-25122, Japanese Laid-open Patent Appln. No. Sho. 57-59563 and Japanese Laid-open Patent Appln. No. Sho. 63-147483) and a method for changing the outer diameter of the shaft rapidly or stepwise (Japanese Laid-open Patent Appln. No. Sho. 57-29374 and Japanese Laid-open Patent Appln. No. Sho. 63-147483) are known in order to adjust the kick point of the fiber-reinforced hollow plastic golf club shaft. However, these methods make the step for manufacturing the shaft complicated and so are not satisfactory as an industrial method. It is also possible to adjust the kick point to a certain degree by changing the fiber winding angle rapidly in an intermediate position. In this case, however, it is difficult to obtain a definite kick point, and moreover, there is a fear that the mechanical strength of the shaft is damaged as the fiber winding angle is rapidly changed.